Process of coating electrodes



Patented Nov. 17, 1925 UNITED STATES- JAMES E. HARRIS, 0] EAST ORANGE. NEW JERSEY, ASQIGNOB TO,

PATENT OFFICE.

' ELECTRIC comm, INCORPORATED, 0! NEW YORK, I. Y., A CORPORATION OF nnw YORK.

PROCESS OI COATING- ELECTRODES.

Io Drawing.

To all whom it may concern:

Be it known that I James E. Harms, a citizen of the United States residm at East Orange, in the county of Essex, tate of New Jersey, have invented certaln new and useful Improvements in Processescf Coatin Electrodes, of which the follow ng is a full, clear, concise, and exact description.

This invention relates to a process I of coating and has particular reference to the coating of filamentary material with a substance capable of thermionic activity for use in vacuum tubes.

An object of the invention is to provlde a process whereby base metal cores may be coated with thermionic material '.-without oxidation.

Another object is to provide a, process whereby substantially all metals may be coated with thermionic material by means.

of a sim 1e and. economical process involvin a bat and electrolytic action.

the older processes which involved baking on the coating in air, it was necessar to use as cores metals such as platinum and other of the noble metals which did not oxidize in air. If certain metal cores such as tungsten, iron,- molybdenum, chromium or alloys thereof are used and the coating is baked in air, it is found that the core metal oxidizes and the oxide forms with the alkaline earth metal compound a stable compound which does not break down into the oxide of the alkaline earth metal when heated in the vacuum bulb. Consequently] no thermionic action ensues.

My present process involves introducing the material to be coated as an electrode in a heated bath of a molten compound or mixture of compounds of the alkaline earth metals, the anode consisting of some material such as carbon which is not readily at: tacked b the electrolyte. The coating is thus app 'ed in the absence of air giving the Application med March 4, m. Serial Io. 868,801.

used at the same time, ual parts are used. The material is then me ted and heated to about 600 degrees C. and a current is passed through the ath using the filamentary material to' be coated as the cathode, with an anode of a bath-resisting material such as carbon. There is deposited on the filament an alkaline earth metal coating of a composltion such that upon exposure to air, it is convertible, in art at least, to alkaline earth metal oxide. t has been found that a cur rent density of about 3.6 amperes per sq. cm. gives very good results especially when platinum is coated in a bath consisting of anhydrous barium chloride.

It has been found that. such metals as iron, nickel, tungsten, molybdenum, and alloys of the same can by this process be coated without the formation of oxides of the metal of the core and the formation of stable com ounds thereof with the alkaline earth meta s. This arises from thefact that the coating takes place in the absence of air. Any compound 0 the alkaline earth metals may be used as a bath, providing it has a melting point sufliciently low for convenience.

What is claimed is:

1. The method of applying an alkalineearth metal oxide coating to a metal, the oxide of which is combinable with alkaline earth metal compounds to form compounds not reducible to alkaline earth metal oxide upon heating in vacuum, said method comprising reparing an electrolyte com osed of an a kahne earth metalcompoun arranging in said electrol a filament of the metal to be coated an electrolytically depositing on said filament an alkaline earth metal coatin which is convertible, in part barium oxide and strontium oxide to a. convertible, in part at least, to barium oxide tungsten filament, said method comprising and strontium oxide upon exposure to air.

preparing an electrolyte composed 0 a ba- In witness whereof, I hereunto subscribe rium compound and a strontium compound, my name this 27th day of February A. D., 5 arranging said tungsten filament in said 1920.

electrolyte and electrolytically depositing on said tungsten filament a coating which is JAMES E. HARRIS. 

